Is it a ZVH?

The Zetec block only has HALF the numbers of oil returns than the CVH block. The Zetec was designed to have the 16v head on it which was all designed to run something like 5w30 engine oil. The CVH head wasn't IIRC.

So you have a bottom end designed to run thin oil and a top end designed to run thicker oil. Have you tried Silkolene Pro S 10w40 or Mobil 1 10w40?

Chances are with you oil smoke when you first fired it up, is oil seeping past the valve guides when parked up over night. Mine used to do it until I had covered a few miles and the guides had beded to the valves (they where all new).

You might have been lucky enough that the oil scraper rings removed enough of the oil on the bores on the way down for the compression rings to bed to the block.